Seventy-five miles north of Las Vegas sits a land parcel in the middle of the desert. Called Area 51, the parcel is just outside of the abandoned Nevada Test and Training Range, where more than 100 atmospheric bomb tests were conducted in the 1950s. Officially, the U.S. government has never acknowledged the existence of Area 51. Unofficially, it has become a place associated with conspiracy theories, alien landings and tiny spaceships.

Journalist Annie Jacobsen tells Fresh Air's Terry Gross that the site has remained classified for many years — not because of aliens or spaceships, but because the government once used the site for top-secret nuclear testing and weapons development.

In Area 51: An Uncensored History of America's Top Secret Military Base, Jacobsen details how several agencies — including the Atomic Energy Commission, the Department of Defense and the CIA — once used the site to conduct controversial and secretive research on aircraft and pilot-related projects, including planes that traveled three times faster than the speed of sound and nuclear-propelled, space-based missile launch systems.

Operation Plumbbob

In the summer and fall of 1957, a series of atmospheric nuclear tests — called Operation Plumbbob — were conducted above ground at the Nevada testing and training range, located just outside of Area 51. Twenty-nine explosions were set off while tests were conducted on troop readiness, accidental detonations and the effects of flying debris on living targets, according to documents declassified by the Department of Energy that Jacobsen details in her book.

During the explosions, security officer Richard Mingus stood guard outside many of the weapons-testing sites, including one with the largest atmospheric bomb that has ever exploded in the United States.

"The bomb goes off. Richard Mingus is at ground zero, safe away in a bunker somewhere, and suddenly someone realizes, 'My God, Area 51 is unsecured,' " Jacobsen says. "And so they send Richard Mingus through ground zero, 45 minutes to an hour after this nuclear bomb has exploded, so that he can get to Area 51 to guard the gate."

Mingus survived, as did many other atomic veterans who stood close to ground zero during other Plumbbob tests.

"You can absolutely drive through an atmospheric bomb test and not be affected," Jacobsen says. "Richard Mingus also stood guard at a test at a subparcel of Area 51 ... [during] a dirty bomb test."

During the dirty bomb test, the Department of Defense and the Atomic Energy Commission simulated a plane crash where plutonium was dispersed on the ground, to see what would happen if an aircraft carrying a nuclear weapon were to crash on American soil. The resulting fallout and structural damage made much of the land uninhabitable.

"The area out at Area 51 that was part of the Operation Plumbbob test continues to be contaminated," she says. "It was not cleaned up until the '80s. And at that point, they sent in men in hazmat suits to scrape the land."

Rockets Into Space With Nuclear Powered Explosions

The nuclear tests at Area 51 gave the Department of Defense ideas about how the technology could be used to help the United States' newly minted space program. And during the space race with the Soviet Union in the 1950s, the Department of Defense proposed using space itself as a weapon, according to declassified documents that Jacobsen found. One of its ideas was to develop a nuclear-powered space-based missile launch system that would sit outside Earth's atmosphere and have the capability to launch missiles — from outer space — into the Soviet Union.

"This didn't end up happening, but it almost did," Jacobsen says. "They were testing the rocket to see whether it would actually work. And to do that meant spewing vast quantities of radiation into the air. It's very controversial [and] it was kept very top-secret."

After the U.S. ratified the 1963 Partial Test Ban Treaty, which prohibited nuclear testing in the atmosphere, the tests continued to take place.

"It comes right up to the edge of violating the treaty when an accident occurs," she says. "In one example, a 148-pound chunk of radioactive debris shoots up into the sky and lands, rending [a subparcel of Area 51] a place that no one could go, not even in a hazmat suit, for six weeks."

The Oxcart

In addition to testing nuclear weapons, Area 51 was often used as a training ground for overhead surveillance planes, says Jacobsen. One plane, called the Oxcart, was designed by the CIA to travel three times the speed of sound at 90,000 feet to spy on the Soviet Union and Cuba.

The Oxcart, in use from 1963 to 1968, worked beautifully, though it was never used over the Soviet Union or Cuba. Never once shot down, it was used in missions over North Vietnam and during the Pueblo Crisis with North Korea.

"It absolutely kept us safer and kept us out of nuclear war," Jacobsen says. "The idea that Area 51 was this test facility working to move science and technology faster and further than any other nation is true and is one of the great hallmarks of Area 51. There are other areas of the base that are controversial — but they both exist simultaneously — out there in the desert."

Annie Jacobsen is a contributing editor at the Los Angeles Times Magazine.

Interview Highlights

The secrecy surrounding Area 51 has made it fertile ground for conspiracy theories, including one about a UFO cover-up and another about the moon landing having never happened. Jacobsen addresses these conspiracy theories in the book and speculates about what led to them. She says her book is based on interviews with 74 individuals with rare firsthand knowledge of the secret base. Thirty-two of the people she interviewed lived and worked at Area 51.

On flying discs and conspiracy theories

"The UFO craze began in the summer of 1947. Several months later, the G2 intelligence, which was the Army intelligence corps at the time, spent an enormous amount of time and treasure seeking out two former Third Reich aerospace designers named Walter and Reimar Horten who had allegedly created [a] flying disc. ... American intelligence agents fanned out across Europe seeking the Horton brothers to find out if, in fact, they had made this flying disc.

"The idea behind it remains, why? Why were they looking for a flying disc? And conspiracy theorists have had their hands on this declassified file for over a decade now, and they say it proves that this flying disc came from outer space. If you read the documents, the takeaway that I found fascinating was that at the end of it, the Army admits finding the Horten brothers, and that the Horten brothers admitted their contact with the Russians and that's where the file ends. Everything after that is classified."

On why Area 51 is actually classified, according to a source

"The Horten brothers were involved in the flying disc crash in New Mexico. And that is from a single source. ... There was an unusual moment where that source became very upset and told me things that were stunning that's almost impossible to believe at first read. And that is that a flying disc really did crash in New Mexico and it was transported to Wright-Patterson Air Force Base, and then in 1951 it was transferred to Area 51, which is why the base is called Area 51. And the stunning part of the reveal is that my source, who I absolutely believe and worked with for 18 months on this, was one of the engineers who received the equipment and he also received the people who were in the craft.

"The people were, according to the source, were child-sized pilots, and there's a lot of debate about how old they were. He believes they were 13, although other people believe they may have been older. But this is a firsthand witness to this, and I made a decision to write about this in the very end of the book, after I take the traditional journalist form of telling you everything in the third person, I switch and I kind of lean into the reader and I say, 'Look, this is not why Area 51 is classified to the point where no one in the government will admit it exists. The reason is because what one man told me.' And then using the first person, I tell you what I was told. And there's no doubt that people are going to be upset, alarmed and skeptical of this information, but I absolutely believe the veracity of my source, and I believe it was important that I put this information out there because it is the tip of a very big iceberg."

On the Soviet human experiments her source told her about

"The child-sized aviators in this craft [that crashed in New Mexico] were the result of a Soviet human experimentation program, and they had been made to look like aliens a la Orson Welles' War of the Worlds, and it was a warning shot over President Truman's bow, so to speak. In 1947, when this would have originally happened, the Soviets did not yet have the nuclear bomb, and Stalin and Truman were locked in horns with one another, and Stalin couldn't compete in nuclear weaponry yet, but he certainly could compete in the world of black propaganda — and that was his aim, according to my source. ...

"What is firsthand information is that he worked with these bodies [of the pilots] and he was an eyewitness to the horror of seeing them and working with them. Where they actually came from is obviously the subject of debate. But if you look at the timeline with Josef Mengele, he left Auschwitz in January of 1945 and disappeared for a while, and the suggestion by the source is that Mengele had already cut his losses with the Third Reich at that point and was working with Stalin."

On why the Soviets would have undertaken such a hoax

"The plan, according to my source, was to create panic in the United States with this belief that a UFO had landed with aliens inside of it. And one of the most interesting documents is the second CIA director, Walter Bedell Smith, memos back and forth to the National Security Council talking about how the fear is that the Soviets could make a hoax against America involving a UFO and overload our early air-defense warning system, making America vulnerable to an attack."